First-principles prediction of free-electron screening of the electron-hole interaction in hybrid perovskite MAPbI₃

Hybrid organic-inorganic perovskite MAPbI₃ has captivated the solar cell community as a high-efficiency photovoltaic material. Recent reports find high intrinsic charged defect concentrations in MAPbI₃ which donate free electrons to the material. Due to these, the Coulomb potential between electrons and holes is further screened and the exciton binding energy decreases. We use first-principles methods based on many-body perturbation theory to determine the influence of free-electron screening on the predicted excitonic properties and the optical spectrum of MAPbI₃. Electronic band structures and gaps are predicted using Hedin’s GW approximation, including the spin-orbit interaction. Electron-hole excitation energies and optical spectra are calculated using the Bethe-Salpeter framework. Our calculations show that exciton binding energies span the experimentally observed range of 31 to 2.5 meV as the free-electron concentration varies between 10¹² and 10¹⁹ cm^-3. The corresponding optical spectra are found in good agreement with experimental results, suggesting that free-carrier screening plays an important role in the optical response of MAPbI₃.